Hi all,i've made a simple circuit to control a pc fan.The circuit is based on an ATtiny85, which measures the voltage on its Pin3 and then sends a corresponding pwm signal to the fan.

I control the voltage on Pin3 via an OUT1000, where 0V is OFF and 4.2V equals 100% power. This works great so far

There is just one thing i can't explain to myself:When trying different voltages via the Phidget-Tool i get several "Voltage Errors" at around ~3.0V. This error occurs when there is a voltage drop because of a higher current draw. But since i'm just measuring the voltage, there should be no higher current draw To be clear, the ATtiny only measures the adjacent voltage on its Pin3. The fans power comes from one separate 12V source, which also powers the ATtiny itself.